It has been discovered that micromotion, movement of an implant relative to the bone it is implanted in, can induce bone absorption around the implant and lead to failure. See Trisi, et al, Implant micromotion is related to peak insertion torque and bone density. Clin. Oral. Impl res, 20 (2009) pp 467-71. This movement is believed to destroy the new cells forming in the gap between the bone and implant. In which event, the tendency is for the bone to resorb around the implant to provide a perceived need for clearance. This leads to weakening and potential failure of the implant. To reduce failure, there is a need for an implant which has very high initial stability. To maximize success of dental implants, the micromotion should not exceed 50-100 μm at the implant/bone interface. Pillar, et al., Clin Orthop Relat Res. 1986 July; (208):108-13.
Implants which are designed for a tight fit in the bone generally require significantly more torque to insert.
Implants for insertion into living bone, including screw type implants are widely used and are well known in the art. Such implants may be used in dentistry or orthopedics. The screw tapping implants generally fall into the category of self-tapping implants and non-self tapping implants. Non-self tapping implants are merely threaded and are screwed into the bone after it is separately drilled and tapped. Self tapping implants contain cutting threads analogous to those in a metal tap which cut threads into the bone when inserted in a drilled hole that is smaller than the self tapping implant diameter. The basic structure of both types of implants comprise a generally cylindrical main body that has a set of external screw threads on the outer surface which engage with threads cut into the bone. The engagement of the threads provides for initial stabilization for the implant. With both types of implants, long term stability is provided by growth of new bone around the implant. A non self-tapping implant is usually tapered at the end which is inserted into the bone. The other end of both implants contains a means for attaching a dental prosthesis such as a tooth and is often threaded to facilitate attachment of the prosthesis.
Self-tapping implants usually contain a more pronounced taper at the end of the implant on which the cutting threads of the tap portion of the implant are disposed.
Self tapping devices of the prior art suffer from a number of drawbacks. The thread cutting abilities of present devices are limited due to the thickness of the threads which creates large amounts of bone chips as part of the cutting process. Current designs are unable to effectively clear these bone chips from the hole. Many devices contain flutes which are substantially parallel to the body of the implant and adjacent to cutting surfaces to aid in clearing bone. The collection of chips results in an increase in the torque required to seat a self tapping implant. The increase in torque adds to patient discomfort and may also lead to breakage of the threads cut in the bone. The inability of the implant to clear debris can also prevent a surgeon from properly seating an implant. The seating and insertion torque problems increase as the length of the implant increases.
Self tapping implants of the present invention are also ideally suited for osseointegrated hearing aids. Designs in the art suffer from slow or weak osseointegration. Movement of the implant further contributes to resorption of bone in the vicinity of the implant. Existing implants also get loose due to mechanical loading on the implant.
The art contains examples of implant designs having grooves within the cutting surfaces for removing debris.
Published United States patent application US20080187886A1 discloses a self tapping dental implant having a vertical groove for collecting debris.
Published United States patent application US20080160483A1 discloses a self tapping implant having a vertical groove for collecting debris.
Published United States patent application US20080131840A1 discloses a self tapping implant having a groove for holding debris.
Published United States patent application US20080081316A1 discloses a self tapping implant having a vertical groove for containing debris.
Published United States patent application US20080038693A1 discloses a self tapping implant having a vertical groove for containing debris.
U.S. Pat. No. 7,281,925 and published United States patent application US20080032264A1 disclose a self tapping implant having a groove cut within and parallel to the self tapping threads for containing debris.
Published United States patent application US20080014556A1 discloses a self tapping implant having a groove running with the threads for containing debris.
U.S. Pat. No. 7,273,373 discloses a self tapping implant having a groove for containing debris and protrusions to aid in anchoring.
Published United States patent application US20070190491A1 discloses a self tapping implant which is out of round and has breaks in the self tapping threads for passage of debris.
Published United States patent application US20070099153A1 discloses a self tapping implant having a substantially vertical groove in the self tapping threads for passage of debris.
Published United States patent application US20040121289A1 discloses a self tapping implant having a substantially vertical groove running in an opposite direction to the cutting threads for passage of debris.
U.S. Pat. No. 6,604,945 discloses a self tapping implant having a substantially vertical groove running for passage of debris.
Published United States patent application US20020102518A1 discloses an implant having a vertical groove for passage of debris.
U.S. Pat. No. 6,273,722 discloses an implant with helices running in opposite directions. However, this is not a self tapping implant.
U.S. Pat. No. 5,984,681 discloses a self tapping implant having open threads and a separate anchor.
U.S. Pat. No. 5,871,356 discloses an implant having vertical grooves for the passage of debris.
U.S. Pat. No. 5,601,429 discloses an implant having grooves for clearing debris running in the same direction as the cutting grooves.
U.S. Pat. No. 4,498,461 discloses an osseointegrated hearing aid.
U.S. Pat. No. 7,116,794 discloses an implant for anchoring a hearing aid.
It has been discovered that micromotion, movement of an implant relative to the bone it is implanted in, can induce bone absorption around the implant and lead to failure. See Trisi, et al, Implant micromotion is related to peak insertion torque and bone density. Clin. Oral. Impl res, 20 (2009) pp 467-71. To reduce failure, there is a need for an implant which has very high initial stability. However, implants which are designed for a tight fit in the bone generally require significantly more torque to insert. Despite the above examples, there is still a need in the art for a self threading implant which is easy to install yet offers acceptable holding power.